The present invention relates generally to radio frequency antenna arrangements, and more specifically, but not exclusively, to a reflector arrangement for attachment to a wireless communications terminal to increase antenna gain for transmission and reception of microwave frequency radiation in a wireless communications system.
Modern wireless communications systems place great demands on the antennas used to transmit and receive signals. In particular in a fixed wireless access system, in which a wireless terminal known as customer premises equipment may be installed at a determined orientation for communication with a base station, it may be required that an antenna produces a radiation pattern that has well defined directional characteristics so as to reduce path loss to the base station and to minimise interference to neighbouring systems, but there is also a requirement that the antenna be small, and cheap to produce.
Typically, a wireless communications terminal may be provided with an internal antenna, situated within the housing of the terminal. The internal antenna is typically designed to have sufficient gain for the majority of deployment scenarios and is designed as a trade-off between the requirements of providing high enough gain to provide a reliable link, and a low cost of manufacture and small size. The internal antenna may be a patch antenna, which may comprise a sheet of metal known as a patch radiator, disposed in a substantially parallel relationship to a ground plane. However, in some deployment scenarios, for example when the customer premises are far away from the base station, there may be a requirement for more gain than the internal antenna is designed to provide.
In order to provide more gain, the terminal may be fitted with an external device to increase antenna gain by decreasing the beamwidth of the radiation beam from the terminal. In one such arrangement, the terminal may be used to illuminate a parabolic dish reflector, which is arranged to produce a beam with a narrower beamwidth than that produced by the terminal. The terminal may be supported on an arm extending forwards of the dish, offset to one side of the dish so as not to block radiation from the dish. However, such arrangements are typically bulky and require the orientation of a terminal that has already been installed to be changed.
In an alternative arrangement to improve antenna gain, the terminal may be fitted with a device that has a dish reflector and a microwave feed assembly comprising two antennas connected together by a transmission line. One of the two antennas is a coupling antenna used to couple radio frequency signals to and from the internal antenna in the terminal. The other antenna is a feed antenna, typically a dipole, used to illuminate the reflector dish so that the dish reflector may produce a beam with a narrower beamwidth than that produced by the terminal. The coupling antenna may be a patch antenna, and is typically held close against the housing of the terminal in front of the internal antenna. However, this arrangement may not present a good impedance match to the transmitter in the terminal, so that signals may be reflected back into the power amplifier, potentially causing distortion of transmitted signals. Furthermore, the arrangement may be bulky and expensive to manufacture.
In another alternative arrangement, a dielectric lens may be fitted to the terminal in front of the internal antenna to increase antenna gain. However, this typically requires the use of large amounts of potentially expensive material, and may add significantly to the weight of the terminal.
It is an object of the invention to mitigate the problems of the prior art.